The present invention relates to a method and apparatus for casting articles from metal foam. More specifically, the invention provides a method of casting articles using a low pressure method of introducing metal foam into a die cavity.
Low pressure casting processes are commonly known in the art. Generally, these processes involve an apparatus including a die and a bath containing a molten metal, such as aluminum. The die and bath are fluidly connected with a riser tube. In the known method, the molten metal is forced upwardly through the riser tube, the tube having its lower end extending below the level of molten metal in the bath and having its upper end connected to an aperture in the die cavity. The molten metal is raised by applying gaseous pressure to the molten metal in the bath. The molten metal then rises up the riser tube and into the die cavity, where the metal solidifies. The gaseous pressure is then reduced allowing excess molten metal to fall back down the riser tube and into the bath. The casting is then allowed to cool further, after which the die cavity is opened to remove the casting therefrom. This process results in a solid article made of the metal. Examples of such low pressure casting are provided in U.S. Pat. Nos. 4,860,820 and 4,875,518 and Japanese application publication number 58003769.
In the manufacture of products such as automobiles etc., there is a high demand for components to be made from materials that have a high strength to weight ratio. In order to meet this demand, much emphasis has been placed on finding materials that are considerably low in weight yet maintain the required structural strength. One such material that has been proposed is foamed metal, such as foamed aluminum. Various methods have been proposed for producing metal foam such as in U.S. Pat. Nos. 5,221,324 and 5,622,542. These methods generally involve the bubbling of a gas through a bath of molten metal, thereby creating a metal foam above the bath. The foam is then drawn off the bath and cooled to form a slab. The slab is then cut or worked to form a desired article. The molten metal normally includes additives such as a metal matrix composite (MMC) and preferably other components such as refractory particles and stabilizers etc. to ensure that the foam generated by the process is preserved. That is, the additives are provided to facilitate the stabilization of the cells comprising the foam.
A need exists for a method of forming a metal foam article using a casting type process.